Central and peripheral aspects of hypothalamic-pituitary-adrenal (HPA) axis dysfunction

An aberrant regulation of the hypothalamic-pituitary-adrenal (HPA) axis is closely associated with the pathophysiology of affective disorders such as major depression (MD). Accordingly, patients suffering from MD frequently show profound neuroendocrine alterations with hyper- or hypo-cortisolism as a result of a dysregulated stress hormone system. Focussing on this key endophenotype of MD, the ‘stress reactivity’ (SR) mouse model was recently established, consisting of three independent mouse lines, the high (HR), intermediate (IR) and low (LR) stress reactivity line, selectively bred for differences in their corticosterone (CORT) secretion in response to a psychological stressor. Previous studies revealed distinct differences between HR, IR and LR animals regarding sleep architecture, activity rhythms, emotional behaviour, cognition as well as neuroendocrine functions, resembling several endophenotypes observed in depressed patients. In the series of studies presented in this work, we aimed to investigate whether the differences between HR, IR and LR mice were restricted to the peripheral phenomenon of adrenal CORT secretion, or whether these endophenotypes were brought about by an aberrant regulation of upstream control centres of the HPA axis. To this end, we performed experiments investigating all functional levels of HPA axis control, i.e. the adrenals, the pituitary and brain centres known to be involved in the neuroendocrine stress response. Moreover, we assessed the expression of corticosteroid-binding globulin (CBG), which contributes to the transport and delivery of CORT to its target tissues. Finally, we studied HPA axis regulatory mechanisms by means of the combined dexamethasone/corticotropin-releasing hormone (Dex/CRH) test. At the level of the adrenal, we found that pharmacological inhibition of the biosynthesis and secretion of CORT using metyrapone had a significant impact on the stress-coping behaviour of HR, IR and LR animals as determined in the forced swim test (FST). As another peripheral factor influencing the secretion of CORT, we assessed the adrenal sensitivity of the animals to adrenocorticotropic hormone (ACTH) in vivo. After a Dex-mediated inhibition of endogenous ACTH release from the anterior pituitary, LR animals showed a markedly reduced CORT surge compared to HR mice in response to a stimulation of the adrenals with two doses of exogenous ACTH, indicating an enhanced adrenal sensitivity in HR mice and a blunted responsiveness to ACTH in LR mice. In addition, we found significant differences in plasma CBG levels between the three mouse lines (HR>IR>LR), concomitant with differences in free plasma CORT both, basal and in response to 15 min restraint stress (HR>IR>LR). Since only free CORT is biologically active, these results indicate that CBG might play a role in the endophenotypes of the SR mouse lines. At the pituitary level, we detected significantly altered ACTH protein levels (HR>IR≥LR) and proopiomelanocortin mRNA expression (HR>IR>LR), suggesting a differential activation of the anterior pituitary between the three lines, which is in line with the observed differences in stress reactivity. In the brain, we assessed the neuronal activation induced by an acute stressor in regions known to be involved in HPA axis function such as the prefrontal cortex, the basolateral amygdala, the hippocampus and the paraventricular nucleus of the hypothalamus (PVN) using c-fos in-situ hybridisation. Acute stress exposure markedly increased neuronal activation in all investigated brain areas. However, significant differences in the neuronal excitation between the three lines were only detected in the PVN (HR>IR>LR), indicating an altered activation of the animals’ HPA system orchestrated by this nucleus. Finally, we assessed HPA axis regulatory mechanisms by means of the Dex/CRH test. Our results revealed considerable similarities to clinical studies, with HR mice showing signs of Dex non-suppression in addition to an overshooting CORT surge after CRH stimulation, mirroring the HPA axis hyper-active state of patients suffering from the psychotic or melancholic subtype of MD. In contrast, LR animals presented a strong Dex-induced CORT suppression and a blunted response to the CRH stimulation, resembling the situation observed in atypically depressed patients. Strikingly, chronic fluoxetine (Flx) treatment enhanced the negative feedback regulation of the HPA axis in all three lines of the SR mouse model. In particular, the Dex-mediated CORT suppression in HR mice was restored by Flx. Furthermore, Flx affected the stress-coping behaviour of the animals in the FST. Flx induced a reduction in active coping, indicating an attenuation of the hyper-aroused state, particularly in HR mice. Taken together, the series of studies presented here demonstrated that the SR mouse model shows functional alterations on all levels of the HPA axis - peripheral, central and regarding the regulation – similar to the endophenotypes of MD patients, thus revealing a high level of face and construct validity of the model. Hence, the SR mouse model can serve as a valuable tool in the discovery and validation of new drug targets and improve already existing treatments of MD, particularly those targeting the HPA system

Dendritic Morphology of Hippocampal and Amygdalar Neurons in Adolescent Mice Is Resilient to Genetic Differences in Stress Reactivity

Many studies have shown that chronic stress or corticosterone over-exposure in rodents leads to extensive dendritic remodeling, particularly of principal neurons in the CA3 hippocampal area and the basolateral amygdala. We here investigated to what extent genetic predisposition of mice to high versus low stress reactivity, achieved through selective breeding of CD-1 mice, is also associated with structural plasticity in Golgi-stained neurons. Earlier, it was shown that the highly stress reactive (HR) compared to the intermediate (IR) and low (LR) stress reactive mice line presents a phenotype, with respect to neuroendocrine parameters, sleep architecture, emotional behavior and cognition, that recapitulates some of the features observed in patients suffering from major depression. In late adolescent males of the HR, IR, and LR mouse lines, we observed no significant differences in total dendritic length, number of branch points and branch tips, summated tip order, number of primary dendrites or dendritic complexity of either CA3 pyramidal neurons (apical as well as basal dendrites) or principal neurons in the basolateral amygdala. Apical dendrites of CA1 pyramidal neurons were also unaffected by the differences in stress reactivity of the animals; marginally higher length and complexity of the basal dendrites were found in LR compared to IR but not HR mice. In the same CA1 pyramidal neurons, spine density of distal apical tertiary dendrites was significantly higher in LR compared to IR or HR animals. We tentatively conclude that the dendritic complexity of principal hippocampal and amygdala neurons is remarkably stable in the light of a genetic predisposition to high versus low stress reactivity, while spine density seems more plastic. The latter possibly contributes to the behavioral phenotype of LR versus HR animals

Solving patients with rare diseases through programmatic reanalysis of genome-phenome data.

Funder: EC | EC Seventh Framework Programm | FP7 Health (FP7-HEALTH - Specific Programme "Cooperation": Health); doi: https://doi.org/10.13039/100011272; Grant(s): 305444, 305444Funder: Ministerio de Economía y Competitividad (Ministry of Economy and Competitiveness); doi: https://doi.org/10.13039/501100003329Funder: Generalitat de Catalunya (Government of Catalonia); doi: https://doi.org/10.13039/501100002809Funder: EC | European Regional Development Fund (Europski Fond za Regionalni Razvoj); doi: https://doi.org/10.13039/501100008530Funder: Instituto Nacional de Bioinformática ELIXIR Implementation Studies Centro de Excelencia Severo OchoaFunder: EC | EC Seventh Framework Programm | FP7 Health (FP7-HEALTH - Specific Programme "Cooperation": Health)Reanalysis of inconclusive exome/genome sequencing data increases the diagnosis yield of patients with rare diseases. However, the cost and efforts required for reanalysis prevent its routine implementation in research and clinical environments. The Solve-RD project aims to reveal the molecular causes underlying undiagnosed rare diseases. One of the goals is to implement innovative approaches to reanalyse the exomes and genomes from thousands of well-studied undiagnosed cases. The raw genomic data is submitted to Solve-RD through the RD-Connect Genome-Phenome Analysis Platform (GPAP) together with standardised phenotypic and pedigree data. We have developed a programmatic workflow to reanalyse genome-phenome data. It uses the RD-Connect GPAP's Application Programming Interface (API) and relies on the big-data technologies upon which the system is built. We have applied the workflow to prioritise rare known pathogenic variants from 4411 undiagnosed cases. The queries returned an average of 1.45 variants per case, which first were evaluated in bulk by a panel of disease experts and afterwards specifically by the submitter of each case. A total of 120 index cases (21.2% of prioritised cases, 2.7% of all exome/genome-negative samples) have already been solved, with others being under investigation. The implementation of solutions as the one described here provide the technical framework to enable periodic case-level data re-evaluation in clinical settings, as recommended by the American College of Medical Genetics

Silicon oxide nanolayers for soft X-ray optics produced by plasma enhanced CVD

Hamelmann F, Aschentrup A, Schmalhorst J-M, et al. Silicon oxide nanolayers for soft X-ray optics produced by plasma enhanced CVD. JOURNAL DE PHYSIQUE IV. 2001;11(PR3):431-436.We have studied the suitability of Plasma Enhanced Chemical Vapor Deposition (PECVD) to produce ultrasmooth silicon oxide layers ranging in thickness from some nanometers to some 10 nm. A tight process control of the layer thickness, layer density and microroughness of the growing film is required. We deposited silicon oxide on silicon wafers, float glass and superpolished quartz substrates. In a remote plasma enhanced CVD process, we used tetraethylorthosilicate (TEOS, Si(OC2H5)(4)) as precursor. Films with a thickness of some 10 nm were produced at different deposition parameters and characterized by in-situ soft X-ray reflectivity, hard X-ray diffraction and auger electron spectroscopy. Best results could be found for the deposition using TEOS in oxygen plasma. In case Of SiO2 layers deposited on standard glass substrates signifcant roughness smoothing was obtained

Experimental realization of a semiconducting full-Heusler compound: Fe2TiSi

Meinert M, Geisler M, Schmalhorst J-M, et al. Experimental realization of a semiconducting full-Heusler compound: Fe2TiSi. Physical Review B. 2014;90(8): 85127

Antidepressant treatment differentially affects the phenotype of high and low stress reactive mice

Modelling key endophenotypes can be a powerful approach to gain insight into mechanisms underlying the aetiology and pathophysiology of neuropsychiatric disorders. Based on evidence of stress hormone system dysregulations in depression, the Stress Reactivity (SR) mouse model has been generated by a selective breeding approach for extremes in HPA axis reactivity, resulting in high (HR), intermediate (IR) and low (LR) reactive mice. The characterisation of their phenotypic alterations has highlighted many similarities of HR and LR mice with the melancholic and atypical depression, respectively. We therefore aimed to examine whether the antidepressant fluoxetine (10 mg/kg/day i.p., 4–5 weeks) can ameliorate the phenotypic characteristics of HR and LR mice in neuroendocrine functions (HPA axis basal activity, stress reactivity, negative feedback), emotional reactivity/coping-strategy (open field, forced swim tests), spatial learning/memory (Morris water-maze) and hippocampal neurogenesis. Line differences in HPA axis reactivity were maintained under fluoxetine treatment. However, we observed fluoxetine effects on glucocorticoid-induced negative feedback, stress-coping behaviours, cognitive functions and neurogenesis. Specifically, our results revealed line-dependent consequences of fluoxetine treatment: (1) an amelioration of the ‘melancholic-like’ features of HR mice (reversing the negative feedback resistance, the hyperactive coping style and the memory deficits; increasing hippocampal neurogenesis); (2) an exacerbation of the phenotypic deviations of LR mice (increasing their pronounced negative feedback and passive coping style). Thus, these findings support the predictive validity of antidepressant treatment in the HR mouse line and emphasize the translational value of the SR mouse model for the development of therapeutic strategies based on endophenotype-driven classifications